The playful North American river otter is equally at home in the water and on land. It makes its home in a burrow near the water's edge, and can thrive in river, lake, swamp, or estuary ecosystems. Otter abodes feature numerous tunnels—one of which usually allows them to come and go from the water.

These otters swim by propelling themselves with their powerful tails and flexing their long bodies. They also have webbed feet, water repellent fur to keep them dry and warm, and nostrils and ears that close in the water. They remain active in winter, using ice holes to surface and breathe. They can hold their breath underwater for some eight minutes.

River otters, members of the weasel family, hunt at night and feed on whatever might be available. Fish are a favorite food, but they also eat amphibians, turtles, and crayfish.

On land, river otters can bound and run quite well, if not quite as effectively as they swim. They love to playfully slide down snow-covered, icy, or muddy hills—often ending with a splash in the water. Otter families of mother and children can be seen enjoying such fun, which also teaches survival skills.

Males do not help raise young otters. Females retreat to their underground dens to deliver litters of one to six young. When the young are only about two months old, they get an advanced swimming lesson—their mother pushes them into the water. Otters are natural swimmers and, with parental supervision, they soon get the hang of it.

These otters' range has been greatly reduced by habitat loss, though they exist in such numbers that they are trapped in some locales. Otters are also very sensitive to environmental pollution.